Although male recombination (MR) elements, mutator genes, and other such factors are often found in natural populations, we still have little information about their frequencies or the effects which they have upon the genetic structure of populations. A very high frequency of male recombination has recently been detected in an Oklahoma population of Drosophila melanogaster. The MR elements appear to have mutor gene activity and preliminary studies support the hypothesis that they break chromosomes. The present proposal is to expand the pilot study. It can be divided into two phases. First, an in-depth survey of Oklahoma populations will be carried out, concentrating upon sampling a variety of industrial and natural habitats. From these samples we can determine the frequency of MR elements and measure associated mutator activity, as well as attempts to determine frequencies of mutator genes not causing male recombination. Frequencies may be correlated with environmental variables, and coupling this with an analysis of the levels of genetic variability, it would be possible to assess the effects of these factors upon the genetic structure of the population. In determining genetic influences, I intend to concentrate upon levels of electrophoretic variability in relatively monomorphic enzymes, though recessive lethals can also be measured easily. The second phase involves laboratory studies to complement the field assays. I intend to ask four main questions: 1) do MR elements break chromosomes (this has been suggested by earlier studies but not yet clearly demonstrated; it implies an increase in lethals through unequal crossover); 2) do they cause a significant increase in somatic mutation or recombination; 3) do they interact with other mutator genes or chemical mutagens; and 4) can MR flies be "cured" by treatments similar to those used against the virus infecting CO2 sensitive Drosophila? All of these questions will clarify the nature of MR elements associated mutator activity, and their effects in natural populations.